1. Field of the Invention
The present invention relates generally to intraocular lenses and more specifically to accommodating intraocular lenses.
2. Description of the Related Art
In a natural eye, the accommodative power, i.e. the ability to (dynamically) vary the focal length of the lens and thus of the eye as a whole, is provided by the reversible deformation of the lens between more and less curved shapes. The natural lens comprises a crystalline lens in a lens capsule or capsular bag. The capsular bag is connected to the so-called zonulae. The zonulae extend generally radially from the lens and are connected with their other end to the ciliary muscle which surrounds the eye essentially in the equatorial plane. The natural lens is generally resilient and strives to a generally more spherical shape.
In the relaxed state of the ciliary muscle its diameter is relatively wide. This causes the zonulae to pull on the capsular bag and to flatten the lens against its resilience. In a young, healthy human eye without refractive errors, this causes the eye to become emmetropic, i.e. having acute vision in “infinity” in a desaccommodated state. Emmetropy is usually determined by having a patient read a predetermined line of an eye-chart from a distance of approximately 5 metres.
When the ciliary muscle contracts, its inner diameter reduces, thus reducing the tension in the zonulae. As a consequence, the natural lens relaxes to assume a shape with a stronger curvature. Thus, the focal power of the lens is increased and the eye can focus on shorter distances, e.g. for reading.
Due to aging or an affliction, the natural lens may lose some or substantially all of its resiliency and only allow accommodation over a limited scope, e.g. resulting in age-related far-sightedness or presbyopia.
Several optical surgery procedures, e.g. cataract surgery, involve the removal of the natural crystalline lens of an eye. In order to install or restore vision to the patient after such surgery an artificial lens may be implanted in the eye. Presently, most implanted artificial lenses have a fixed focal length or are multi-focal lenses having two or more fixed focal lengths. These lens types provide no or at most pseudo-accommodative power. This leaves patients who have underwent such surgery more or less handicapped in everyday life, since they are no longer able to quickly and rapidly focus at any given distance.
When the natural crystalline lens is surgically removed from the lens capsule, the capsular bag may be left essentially intact, in that it can still be deformed by the ciliary muscle if a sufficient counterforce is provided. This functionality can remain even when a substantial window, or rhexis, has been cut out of the capsular bag.
There is thus ongoing research for an artificial intraocular lens or lens system providing accommodative power, especially by using the natural focussing system of the eye, relying on the reversible deformation of the lens, and a number of patent applications and patents discuss accommodating intraocular lenses.
For instance, U.S. Pat. No. 4,994,082, US and 2004/0158322 discuss complex lens systems mounted in a frame wherein the individual lenses move with respect to each other essentially in a plane perpendicular to the optical axis. U.S. Pat. No. 4,994,082 also discusses displacing two lenses along the optical axis.
Furthermore, U.S. Pat. No. 5,275,623, US 2002/0116061, US 2004/0082994 and US 2005/055092 discuss an accommodating intraocular lens comprising a frame and two lenses which are displaced along the optical axis of the lens system and of the eye, wherein the relative motion of the anterior and posterior parts of the capsular bag is used for realising the motion of the lenses.
US 2005/0131535 discusses a deformable intraocular lens in a frame.
It should be noted that U.S. Pat. No. 3,305,294 U.S. Pat. No. 3,507,565, U.S. Pat. No. 3,583,790, U.S. Pat. No. 3,617,116, U.S. Pat. No. 3,632,696, U.S. Pat. No. 3,751,138, U.S. Pat. No. 3,827,798 and U.S. Pat. No. 4,457,592 describe changing the focal length of a lens system comprising two particularly shaped lenses by linearly displacing the lenses with respect to each other.
Using such lenses for intraocular lenses is known from WO 2005/084587, WO 2006/025726, WO 2006/118452 and from Simonov A N, Vdovin G, Rombach M C, Opt Expr 2006; 14:7757-7775.
U.S. Pat. No. 4,650,292 discusses rotating optical elements of a compound lens with respect to each other for changing the focal length thereof, using surfaces described by polynomial equations having a non-zero term of at least fourth order.
Further, U.S. Pat. No. 6,598,606 describes a method for providing a lens implant in a lens capsule with a predetermined refractive value.
In all these prior art (intraocular) lenses and lens system relatively large displacements of the lenses with respect to each other are used for accommodating and/or the intraocular lenses use the equatorial motion of the zonulae and/or capsular bag for effecting accommodation.
It has been found that when an artificial lens has been implanted into the capsular bag, the flexibility of the capsular bag, and thus its accommodative power reduces over time, which effect is usually most pronounced around the equatorial rim of the capsular bag.
Further, it has been found that, in time, cellular growth or migration may cause further stiffening of (the remainder of) the capsular bag and opacification thereof, and consequentially not only loss of accommodative power but also general loss of sight to the patient.